1. Field of the Invention
The invention relates to a device for positioning electronic circuits arranged on a foil, for example chips, on a circuit card, ceramic substrate or the like, using the flip-chip method, whereby the chips are lifted from the foil by needles located under the said foil, and are further picked up by a needle with a suction cup or by a suction cup that rotates the chips by 180xc2x0, and the chips are then received by another needle with a suction cup and positioned on the circuit card for direct connection of the contact lines.
2. Discussion of Background Information
Normally, the electronic circuits or the chips are fixed to the circuit card on the side facing away from the contacts, and the contacts and contact lines are connected with microwires. The wires are connected to the contacts by means of ultrasonic welding, for example. This method is also referred to as wire bonding. This method is disadvantageous because too many steps were required to manufacture the finished circuit board, and the scattering effects are difficult to control.
The flip-chip method is an alternative to the wire bonding. The contacts of the chip are connected directly to the contact lines of the circuit card. This method provides a higher contact reliability, provides shorter contact paths, especially at high frequencies, and eliminates the costly wire bonding. In order to balance the different strain coefficients, the space between the chip and the circuit card is filled with glue or filler after contacting.
With the flip-chip method, it is important that the contacts on the chip and circuit card are positioned exactly on top of each other. In order to achieve this, the position of each chip and each circuit card must be measured and a corrective movement calculated. If the circuit card geometry is precise enough, it is sufficient to measure two reference points on the circuit card, and to calculate the individual positioning points. Otherwise, each individual positioning point has to be measured individually.
A particular problem is the programming of the target position for a chip, since visual correction of the result is not possible. The structures of the chip and the circuit card are located directly on top of each other. The accuracy of the positioning of the contacts can only be verified with destructive methods.
The present invention provides a device of the type mentioned above, which avoids the disadvantages of the prior art, and offers a high degree of user comfort due to programmability and reproducibility of the various settings, and has a simple structure.
The device according to the present invention is characterised by the fact that both the lifting needles used for lifting the chip from the foil and the receiving needle with a suction cup are capable of a synchronous and substantially rectilinear or vertical movement, that the needle with a suction cup is placed in a holder that is mounted in an arm so as to be capable of movement, wherein the arm is driven by a drive in order to carry out the 180xc2x0 rotation movement, and that an additional needle with a suction cup is also mounted in a holder that provides it with four degrees of freedom, namely along the axes x, y, z and rotation about one of the axes.
With the present invention, it is possible to use a motor for both the rotation of 180xc2x0 and the vertical chip pick-up movement, and to control the chip pick-up in such a way that it is synchronous with the movement of the lifting needles. This synchronous pick-up means a significant quality improvement, since the chip is held between the lifting needles and the needle with a suction cup with constant force throughout the entire procedure. Moreover, there is no horizontal relative movement between the lifting needles and the needle with the suction cup, which would inevitably destroy the chip surface.
Furthermore, the present invention makes it possible to produce a mechanical device for extremely rational manufacture and for an increase in the automation of circuit card printing. In addition, the present invention makes it possible to improve enormously the quality of the circuit card thus produced. Another significant advantage is that the structure of the device according to the present invention is very simple and very economical due to the arrangement of only one drive for the movements to position the chip. The freedom of movement of the second needle with a suction cup guarantees a high quality of positioning of the chips on the circuit card.
In accordance with another aspect of the present invention, two stereometric cameras are provided, whereby one stereometric camera is used to measure the circuit card and the other stereometric camera is used to measure the at least one chip, and both stereometric cameras are connected to a computer, and the two stereometric cameras are calibrated by overlaying the image of the chip taken by one camera and the image of the circuit board taken by the other camera until they match, and this calibrated position can be stored on a computer. With the two stereometric cameras, a further increase in quality is achieved. Each circuit card or each substrate is held in position and measured at two points using a stereometric camera. Thereby, a difference from the programmed original substrate may already occur. The recorded definitive values of the circuit card are entered into the computer and stored. The second stereometric camera measures each chip, whereby these values are also entered into the computer. Of course the calibrated position, which is obtained by overlaying the two images, is also stored in the computer.
In accordance with a further aspect of the present invention, the computer calculates or detects possible deviations from the calibrated position after measuring the chip, and controls the second needle with a suction cup in accordance with this difference. With the measurement and registration of the chip data by the second stereometric camera and the corresponding evaluation using suitable software, a programming aid is provided for the positioning of the chip on the circuit card. The second needle with a suction cup is controlled in accordance with the values calculated by the computer. The main advantage is the programmability of control for the device, whereby for example the path, the speed and/or the time or the like can be programmed. Moreover, it is of great advantage that all the values or data are reproducible, especially via the computer unit. The reproducibility of settings is an imperative in such highly specialised technology, in particular in order to guarantee perfect quality.
As already mentioned, the programming of the target position of the chip is particularly difficult in the prior art, since visual correction of the result is not possible.
In order to make this process as simple as possible for the operator, the method according to the present invention has been developed, whereby it is sufficient to overlay the image of the chip structure taken by one camera and the image of the circuit card taken by the second camera until they match. Thereby, the computer automatically calculates the target position for the chip.
In a further embodiment of the present invention, a stepper motor is provided as a drive for the 180xc2x0 rotation movement of the arm. The advantage is that the stepper motor is a mature drive component that requires very little maintenance and can be controlled very accurately with the smallest units of measurement.
In accordance with a further aspect of the present invention, the arm is arranged radially on a shaft, whereby this shaft is mounted in a concentric tubular shaft, and the tubular shaft has a slit for the arm to pass through, with an angle greater than 180xc2x0, preferably 191xc2x0, and the tubular shaft can be driven by the stepper motor via a drive belt. The angle being greater than 180xc2x0 advantageously guarantees that a vertical movement of the needle with a suction cup is possible when picking up the chip from the foil. Moreover, with the arrangement of the arm on a shaft that is mounted in a tubular shaft, a simple and functional design is guaranteed.
In accordance with a special aspect of the present invention, both the shaft and the tubular shaft are fitted with a radial bolt, whereby the bolt in the shaft juts out through the slit or a hole in the tubular shaft and the two bolts are connected by a tension spring. The advantage of this design lies in the fact that the technically simple components guarantee reliable and low-maintenance operation.
In accordance with a further aspect of the present invention, the radial arm arranged on the shaft performs a rotation movement of exactly 180xc2x0, limited by stoppers. For the exact hand-over of the chip from the lifting needles to the needle with a suction cup, and from the needle with the suction cup to another needle with a suction cup, the accurate 180xc2x0 rotation movement is an advantageous basic requirement that guarantees a trouble-free process.
In accordance with a further embodiment of the present invention, the tubular shaft has an additional radial bolt and a holder is fitted with a stopper, whereby the radial bolt sits on this stopper when the arm is in horizontal position. The advantage thereby is that with this simple construction, the rectilinear, precise vertical movement of the needle with the suction cup can be performed in a controlled manner.
In accordance with another aspect of the present invention, the holder is mounted in the arm so as to be capable of movement, against the tension of a spring. The advantage of this design is that a highly technical work process can be performed with technically simple components.
In accordance with a further aspect of the present invention, the holder is mounted in the arm so as to be capable of movement, whereby a spring is provided that is connected to the holder and the radial bolt. The advantage of this design is that a highly technical work process can be performed with technically simple components. In particular, the force acting on the chip via the needle with a suction cup can be defined precisely via the angle of the radial bolt when the arm is lying on the stopper, i.e. the angle in excess of 180xc2x0. This is of advantage since it is more or less a technological necessity to apply greater force to larger chips than to smaller chips. Moreover, the defined application of force is of advantage when different tools are used. When using a rubber tool, greater force will be applied than when using a steel tool. In addition, the force acting on the chip during the pick-up process can be kept more or less constant.
In accordance with another advantageous aspect of the present invention, the spring is a tension spring. This offers the advantage that the distance between the radial bolt and the stopper for the holder on which the radial bolt lies is virtually zero. This also means that the spring always has the same length, so that the force is constant.
In accordance with a further aspect of the present invention, the tubular shaft can be further rotated counter to the force of the tension spring. By driving the tubular shaft with the stepper motor, an accurate and precise control of the movement is possible, whereby the tension spring supports the basic striving of the invention for simplicity, reliability and economy.